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ACC2-3 controller

General description

The ACC2-3 autochange controller is the intelligent part of the system. It handles the communications to and from the CMM controller, controls the ACR1 autochange rack, and multiplexes and interfaces the head and rack probe signals.

Front panel

The following figure shows the arrangement of the ACC2-3 front panel.  Descriptions of the functions of the switch and LEDs follow.

Technical drawing:  Technical drawing:  ACC2-3 front panel - labelled

1  POWER ON LED (green)

Powered from an internal power rail, this LED indicates that the unit is switched on.

2  PROBE SEATED LED (yellow)

Indicates the status of the selected probe.  When the probe interface circuit is active, this LED will be ON. In this condition the LED will be OFF when the stylus is deflected.

NOTE: This LED is only operational when the internal probe interface is selected.

3  RACK READY LED (yellow)

Indicates the status of the rack.  The LED is OFF when the rack is active.  A flashing LED indicates that the system is in datum mode 1 (see 'Operating modes' section, mode 6).

4  RACK ACTIVE LED (yellow) *

Indicates that the rack is performing a lock or unlock procedure.  A flashing LED indicates that the system is in datum mode 2 (see 'Operating modes' section).

5  LOCK ERROR LED (red) *

Indicates that a fault has occurred during a lock or unlock procedure.


Indicates that the rack has been overtravelled or an excessive entry speed condition has been detected.

7  STOP LED (red)

Indicates that the ACC2-3 has asserted the PICS STOP signal following a critical failure.

* Various combinations of these LEDs are used to indicate other fault conditions (see 'Operating modes' section, 'Mode 4 - Error mode).


The RESET switch initiates a complete software restart. It is used for resetting the system after a collision, or for putting the system into or out of datum mode 1 (mode 6). To take effect, the button must be pressed for at least 100 ms.